Refrigerating apparatus



fizz/6722 52 2 Sheets-Sheet 1 F A RICKERT ETAL REFRIGERATINC APPARATUS May 1, 1951 Filed July 12, 1946 1951 F. A. RICKERT ETAL 2,551,153

REFRIGERATING APPARATUS Filed July 12, 1946 2 Sheets-Sheet 2 Patented May 1, 1 951 REFRIGERATING APPARATUS Fred A. Rickert,

Grayslake, and Roy E. Crichton,

Lake Villa, Ill

Application July 12, 1946, Serial No. 683,174

9 Claims.

The present invention relates in general to refrigeration, and has more particular reference to refrigerating apparatus, including heat absorbing means and improved means for accomplishing and controlling the periodic defrosting of the heat absorbing means; the present invention incidentally including improved control means for controlling the operation of the refrigeration apparatus.

An important object of the present invention is to provide refrigerating apparatus, including means forming a heat absorber susceptible of becoming frosted as a result of operation of the absorber, as such, in a moisture containing atmosphere, in combination with means for heating the absorber at intervals for defrosting urposes.

Another important object is to provide refrigerating mechanism, including a cooling unit formed with refrigerant ducts, and operable as a means for absorbing heat from the surrounding atmosphere by a refrigerant in said ducts, the cooling unit being provided with ducts for the circulating of a heating medium therethrough to heat the unit at intervals for defrosting purposes.

Another important object is to provide a refrigerant evaporator unit having ducts therein for an evaporable refrigerating medium, and additional ducts formed in said unit for the circulation of a heating medium for the purpose of defrosting the unit at intervals.

Another important object is to provide refrigerating apparatus, including an element or unit for the absorption of heat from the surrounding atmosphere, whereby the unit may become frosted when in heat absorbing operation in a moisture containing atmosphere, including means associated with said unit for the delivery thereto of a heated defrosting medium for defrosting purposes; a further object being to provide a heater for heating the defrosting medium, and pump means operable to circulate the defrosting medium between the heater and the cooling unit, whereby the latter may be heated and, thus, defrosted by said circulating medium.

Another important object is to provide control means for governing the operation of a defrosting means of the character mentioned operatively associated with a cooling element or unit;

a further object being to provide electrical means for controlling the operation of the cooling unit, and to operate the defrosting means when the cooling unit is not in operation as a heat absorber.

Another important object is to provide defrosting means, including a heater operable to apply heat to a defrosting medium under the control of thermostatic means, whereby to control the temperature of the defrosting medium.

Another important object is to provide control means for defrosting apparatus of the character mentioned, including means for operating a cooling unit with which the defrosting mechanism is operatively associated, and timing means operable to place the defrosting apparatus in operation, at intervals, while stopping operation of the cooling unit, as such.

The foregoing and numerous other important objects, advantages, and inherent functions of the invention will become apparent as the same is more fully understood from the following description, which, taken in connection with the accompanyingdrawings, discloses a preferred embodiment of the invention.

Referring to the drawings:

Fig. 1 is a diagrammatic representation of refrigeratingapparatus provided with defrosting means in accordance with the present invention; and

Fig. 2 shows a modified arrangement of means for controlling the operation of the apparatus shown in Fig. 1.

To illustrate the invention. the drawings show refrigerating apparatus, including heat absorbing means II adapted, when the refrigeration apparatus is in operation, to absorb heat from, and thus refrigerate, the atmosphere surrounding the heat absorbing means II. The absorbing means ll may be of any suitable character, the same preferably comprising a cooling unit formed with duct means therein for containing a heat absorbing refrigerating medium. To this end, the cooling unit may conveniently comprise an evaporator formed with ducts for the reception of an evaporable refrige erant, and any suitable, convenient, or preferred refrigerant evaporator may, of course, be employed. The evaporator, hence, may comprise any means forming a refrigerant duct system in the cooling unit.

As shown, the duct system may comprise duct forming conduit means I2, arranged in coils or loops l3 interconnected in series to form a continuous duct system, through which a suitable evaporable refrigerant may be circulated from an inlet pipe I4 to a discharge pipe l5. Alternately, the duct system may comprise ducts extending in parallel relationship between refrigerant inlet and outlet headers, with which the delivery and discharge pipes l4 and [5 are connected.

The duct system may, also, be enclosed within a suitable housing to be refrigerated, or the ducts may be/form'e'd in, and -as integral parts of, the walls of such housing, in which case the housing itself may comprise the cooling or heat absorb; ing unit. In such case, the refrigerant absorbs medium.

comprise conduit means 20, having portions incliidinig-theldbped portions 2| disposed in spaced heat from the housing walls, which, in absorb heat from the surrounding-atmosphere to'be cooled.

The present invention contemplates the pro vision of means whereby the defrosting operation may be accomplished rapidly, to thereby substantially reduce the defrosting interval, the present invention further providing means whereby the defrosting operation may be accomplished without appreciably impairing the refrigerated condition of the atmosphere within an enclosed storage compartment, in which the cooling unit being defrosted is located.

To this end, the cooling unit is provided with defrosting means operable to supply defrosting heat to the cooling unit. As shown, the defrostingmeans of the present inventionmay comprise duct means formed in the cooling unit for the circulation therethrough of a heated defrosting Said duct means may conveniently relationship-in the cooling unit I l, to form a heat- I ing duct system. This duct system may be con- Any suitable or preferred meansmay be employed for delivering the refrigerating medium to and from the refrigerant ducts forming the cooling unit. As shown; the refrigerant delivery means ma comprise a suitable refrigerant-compressor IS, the inlet orsuc tion side of which may be connected with th discharge pipe 15, the delivery side of the compressor being connected with the refrigerant supply pipe 14, preferably through refrigerantcondensing means I! and refrigerant flow control means l8, said control means 28, in the illustrated embodiment, comprising a refrigerant flow control valve. Suitable means, such as an electric motor l9, may be pro- I vided for driving the compressor.

r When-in operation, the illustrated system functions to draw refrigerant, in evaporated condition, from the-cooling unit ll through the pipe l5 to the suction side of the compressor. The compressor applies pressure to the refrigerating medium in gaseous condition, and delivers the compressed medium to the condenser l1. In passing through the condenser, the refrigerant is cooled and condensedfrom gaseous to-liquid condition. Fronr the condenser l'l the liquid refrigerant may flow, under the control of the valve 18, through the deliver-ypipe-M to the evaporator. Liquid refrigerant, thus delivered in the cooling unit, may therein evaporate and absorb heat when the compressor is in operation.

When the cooling unit is -operated as'a heat absorber in 'a surrounding atmosphere containingmoisture, there is-a-tendency for the cooling unit to become frosted by the condensation and freezing of-moistureupon thecooling unit. After a unit has beenin operation during an extended period, frost may accumulate on'the cooling element to an appreciable-depth, thus impairing its heatabsorbing eificiency. -A s-'a consequence, it is desirable, at intervals, to defrost the ooling element in order to eliminate the efi'lciency impairing f-rost layer. Defrosting may, of course, be accomplished by stopping the operation of the refrigeration apparatus and allowing the surrounding atmosphereto warm the cooling unit to a temperature at which the frost layer melts, tothu's eliminate the same from the cooling unit. Such defrosting,however, consumes an appreciable amount of time, "and'require's that-the temprature of the surrounding atmosphere besub stantially raised, thereby "entirely destroying the refrigerated condition "as in an enclosed-storage chamber, in which the cooling unit being -:defrosted'is located.

nected with inlet and outlet pipes 22 and 23, resp'ective1y,-th1=ough which a suitable fluid heating and'defrosting medium may be circulated to and from the cooling unit, for defrosting purposes. Although the conduit 20 and the several spaced loops-2| thereof comprise a single conduit pipe, in which 'thel'oop's 2| are interconnected in series relationship, it will 'be obvious that the conduit system may include loop's interconnected in parallel relationship, as with inlet and outlet headers, to which the inlet-and outlet pipes 22 and "23 may, respectively, be connected. It 'will, als0,'be obvious that the 'coriduits,'if desired, may be-formed directly in thewalls of the cooling unit, where the same is of walled construction. Suitable delivery means '24 is provided for delivering a-heated defrosting medium through the deliverypipe22 to the cooling unit, for defrosting. purposes. While any suitable or convenient delivery means may be employed, we have illustrated a heater comprising a reservoir 25 adapted -to contain a supply of the defrosting medium' 2'6. Any suitable-fluid may be employed as adefrosting medium, although it is preferable to employ a liquid, such'as brine, or other noncorrosive liquid, which will not freeze at the operating temperature of the cooling unit.

Suitable -'means is .provided for heating the defrosting -medium in'the reservoir 25. While any suitable or convenientheating means may be employed, we prefer -to utilize electrical heating elements 27 of the immersion type, such elements being conveniently mounted in the lower portions of the reservoir 25, in position immersed in -thede'frosting medium 26. The discharge 'pipe 23 may be connected with the reservoir 25, preferably to deliver the defrosting medium discharged from the cooling unit into the reservoir at,or adjacent, the bottom thereof, in position to bere-heated by the heating-elements '21. The-delivery means 24, also, preferably includes a suitable pump 28, preferably 'mounted inthe-upper portions of the reservoir, in position immersed within the defrosting mdiu'm in 'the reservoir, whereby the pump {may d'raw'theheated medium from the reservoir "and discharge the same into and through" the'conduit '22, which is preferably connected directly with the discharge side of the pump "28. Any suitable piunp driving meansmay, be employed for actuating the pump, although weprefer to employ an electricfmotor, 29, which may conveniently be mounted on the reservoir, as at the top thereof, and drivingly connected with the pump.

We also prefer to provide the reservoir with a thermostat 3c in heat exchange relationship with the defrosting medium within the reservoir and adjacent the heaters 27, whereby to regulate the temperature of the defrosting medium in the reservoir. j

From the foregoing it will be seen that when the pump 28 is in operation, the defrosting medium, in heated condition, may be delivered through the conduit 22 to and through the defrosting duct system in the cooling unit, and may be returned thence through the discharge conduit 23 to the reservoir, for re-heating and re-circulation by the pump 28. The circulation of a heated defrosting medium in this fashion through the cooling unit, will warm it rapidly to a temperature at which frost accumulated thereon will melt and drain, in liquid condition, from the cooling unit, which may thus be rapidly defrosted. By heating the cooling unit, for defrosting purposes, in the manner described, the temperature of the surrounding atmosphere need not necessarily be raised to any appreciable extent. As a consequence, the atmosphere within an enclosed chamber, in which the cooling unit is located, may remain substantially in refrigerated condition throughout the defrosting interval.

In conjunction with the cooling unit, a drip pan 3| may be provided, a position immediately beneath the cooling unit, to catch melted liquid draining from the cooling unit during the defrosting interval, and said pan, if desired, may be provided with a drain conduit 32, which preferably extends out of the enclosed chamber of the refrigerator in which the cooling unit is located, whereby to deliver the melted defrosting drippage from the refrigerated chamber.

In order to control the operation of the refrigerating apparatus and the defrosting means, we provide a suitable, preferably electrically actuated, power delivery and control system 33, comprising interconnected control relays electrically interconnected with a suitable source of electrical power and with the control valve [3, the heaters 21, motor 29, and thermostat 30, for the selective control thereof and of the compressor driving motor l3.

If desired, the control system may, also, provide for the operation of a circulating fan 34, for circulating the atmosphere to be cooled to the cooling unit. Such fan is preferably in operation only when the refrigerating apparatus is functioning to cool the atmosphere surrounding the cooling unit, the fan being preferably inoperative during the defrosting operation, to minimize heat transfer from the cooling unit to the surrounding atmosphere during the defrosting period, when the unit is heated by circulation of the defrosting medium through the defrosting conduits.

The control system may, also, include a thermostat 35, disposed in heat exchange relationship with the cooling ducts of the cooling unit, and serving to control the operation of the refrigerating system.

The control system 33, thus, is adapted to selectively deliver power, either to operate the refrigerating apparatus or to operate the defrosting apparatus, and to prevent operation of each apparatus when the other is in operation. To this end, the control system compriseselectrical conductors 36 and 33 adapted fgr connection with a suitable supply of electrical power. Switch means 31 is provided to control the delivery of power from the conductors 36 and 36 to the motor 19. The switch means 3! preferably comprises a relay switch, having an actuating solenoid 38 for selectively connecting the conductors 36 and 36 with the compressor motor 19- for the delivery of operating power thereto, when the solenoid 38 is energized, the switch 31 functioning to disconnect the motor from the power supply conductors 36 and 36 when the solenoid 38 is de-energized.

. Switch means 39 is, also, provided to control the delivery of power from the conductors 38 and 36' to the heaters 2? and the motor 29, for the operation of the defrosting apparatus. The switch means 39 preferably comprises a relay switch, having an actuating solenoid 40 for selectively connecting the conductors 36 and 36 with the heaters 2! and the pump motor 29, for the delivery of operating power thereto, when the solenoid dB is energized, the switch 39 functioning to disconnect the heaters 21 and motor 29 from the conductors 36 and 36' when the solenoid 40 is cle-energized.

In order to energize the solenoids 38 and 40 selectively and alternately, to operate the refrigerating apparatus or the defrosting apparatus, one side of each of said solenoids is directly connected with the conductor 36, the other sides of said solenoids being connected through the contacts of a preferably single pole, double throw switch 4! with the conductor 36. The switch 4| preferably comprises arelay switch, having an operating solenoid 42 which, when energized, may complete a circuit through the contacts of switch 4! to energize the solenoid 40, and thereby place the defrosting apparatus in operation. When the solenoid d2 is de-energized, however, the switch All may complete a circuit to actuate the solenoid 38 and, thus, place the refrigerating apparatus in operation.

The solenoid 42 is connected in a series circuit between the conductors 36 and 36, said circuit including the normally open switch 43 of a timing device M, including clock mechanism 45 which may be actuated by a preferably constant speed induction motor connected with the conductors 36 and 36. The clock mechanism 45 may be provided with means for closing the switch 43, at intervals, and to hold said switch closed during the defrosting period; and, of course, the clock mechanism may be adjustable to vary the defrosting period and the interval between successive defrosting operations.

So long as the switch '43 remains closed, the solenoid 42 will remain energized, thus controlling the switch 4| to hold the solenoid 38 in deenergized condition, to thereby inactivate the refrigerating apparatus. So long as the solenoid 42 remains energized, however, the switch 4! will condition the circuit, including the solenoid 40, to deliver operating power through the switch 39 to the heater 2? and the motor 29. This circuit, however, may include the thermostatic switch means 33, which will be closed so long as the temperature of the defrosting medium remains below a preselected maximum temperature. Should the temperature of the medium rise above said preselected maximum temperature, the thermostatic switch means 30 will open the circuit to the solenoid 40, thereby disabling the heaters '21 and the pump 28. The preselected maximum temperature, at which the switch means 30 is set to open, may be, and preferably is,"

sohigh as to holdthe switch 3llclosed'duringznormal defrosting operations,.and until all frost has removed from the cooling unit. After the unit, however, has been completely defrosted, there being no frost remaining to'rapidly absorbheat from the defrosting medium circulating in the defrosting ducts of the cooling unit, the defrosting medium will be returned to the reservoir 25 at relatively high temperature, so that the thermostatic switch 30 may function to discontinue operation of the defrosting apparatus, even though the defrosting period, as determined by the timing mechanism 44, may not have terminated.

In additiontothe compressor motor l9, operation of the refrigerating apparatus includes the refrigerant flow control valve I8 and the air circulating fan 34, the valve |8 beingpreferably of the normally closed, electrically energized to open type. These elements H3 and 34 may conveniently be interconnected in parallel relationship with the operating solenoid38 of the motor control relay switch, so that the valve l8 and the motor 34 are energized, with the motor l9, under the control of the switch means 4|, whenever the actuating solenoid 42 of said switch means 4| is de-energized' during the extended intervals between defrosting operations, as determined by the timing means 44.

It is, also, desirable to provide means for controlling the operation of the refrigerating apparatus during such operating intervals, between successive defrosting periods, in accordance with the refrigeratedtemperature at the cooling unit H, or within the refrigerated chamber in which the unit is disposed. To this end, the elements I8, 34, and 38, which are interconnected in paralled, may be connected in series with the thermostatic switch 35, which is normally closed so long as the refrigerated temperature produced by the cooling unit remains above a predetermined minimum temperature. The thermostatic switch, however, is adapted to open and, thus, disable the elements I8, 34, and 38 to stop operation of the refrigerating apparatus, when the refrigerated temperature produced by the unit I reaches such selected minimum. The thermostatic switch means 35 may be of adjustable character to enable the same to be set to open at any selected low temperature.

Obviously, numerous modifications may be made in the control mechanism and the manner of interconnecting the relay switches and the operating solenoids thereof, for the control of the elements l8, I9, and 34 of the refrigerating apparatus, and the elements 37, 29, and 30 of the defrosting apparatus. For example, the adjustable thermostatic switch could be connected to control the operation of the solenoid 38, whereby to control the compressor motor IE! only, the devices l8 and 34 remaining in operation so long as the solenoid 42 remains de-energized. Alternately, the thermostatic switch 35 could be connected to control the operation of the valve l8, or said valve could be controlled, independently of the elements 34 and 38, but in parallel relationship therewith, by suitable switch means responsive to refrigerant pressure at the discharge side of the condenser H.

In Fig. 2 of the drawings is shown a modified control system, including control equipment in addition to that shown in Fig. 1. In order that theheaters 21 of the defrosting apparatus may be placed in operation to bring the defrosting medium to a desired temperature, for defrostingpurposes, before the circulating pump 28is placed in operation during this preliminary heating period, the refrigerating apparatus is maintained in operation, and is stopped only when the circulating pump 28 is started. To this end, the control equipment may include, in addition to'the equipment shown in Fig. 1, a normal- 1y open solenoid switch 46, having an operating solenoid 41 to close said switch when the solenoid is energized. The solenoid-is interconnected in circuit with the switch 43 of the timing mechanism, and in parallel relationship with the actuating solenoid 42 of the switch means 4|. The switch 46 controls a series circuit extending between the conductors 36 and 36, and including the heating means 21. If desired, the heating means may be connected in series with a thermostatic switch 48. The actuating solenoid 42 0f the switch means 4| is in series with thermostatic switch'49, the circulating pump motor 29 alone being controllingly connected with the switch means 39.

The thermostatic switch means 48, like the switch means 30, is adapted to remain normally closed so long as the temperature of the defrosting medium in the reservoir 25 remains below a preselected maximum temperature, and to open whenever such-maximum temperature is reached or exceeded. The thermostatic switch means 49, however, is adapted to remain normally open, and to close when the temperature of defrosting medium in the reservoir 25 reaches, or exceeds, a minimum temperature suitable for defrosting circulation to the cooling unit. Accordingly, upon closure of the timing switch 43, the solenoid 47 will be energized to close the switch 46 and place the heaters 21 inoperation. Since at such time the defrosting medium may be substantially cold, the thermostatic switch 49 will remain open, whereby the solenoid 42 will be de-energized and the switch 4| will maintain the refrigerating apparatus in operation. As soon as the defrosting medium in the reservoir 25 reaches the desired defrosting'temperature, the switch 49 will close, energize the solenoid 42, and, by operation of the switch means 4|, disable the refrigerating apparatus and place the circulating pump motor 29 in operation, by energizing the solenoid 40. 'I'hereupon, the defrosting medium, at suitable defrosting temperature, will be circulated to the cooling unit. The heater 21, however, will be maintained in operation, most eificiently, to maintain the defrosting medium at a suitable temperature, and will immediately go out of operation by opening of the switch means 48, in the event that such temperature is exceeded at any time during the defrosting operation. If desired, a thermostat, like the thermostat 30 in Fig. 1, may be applied in the system, as shown-in Fig. 2, and connected in series with the solenoid 40 to stop'operation of the circulating pump, as when the temperature of the defrosting medium rises in the reservoir 25 to a point indicating that frost has been completely removed from the cooling unit. Such thermostatic switch means, if desired, may be incorporated as a second switch in the thermostatic means 48.

It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description, and it is obvious that numerous changes may be made in theform, construction and arrangement of the several parts without departing from the spirit or scope of the invention, or sacrificing any of its The invention is hereby claimed 'as follows! l. A refrigerating apparatus having a cooling unit susceptible of becoming frosted, defrosting means comprising a duct system for the applica tion of a defrosting fluid in heat exchange relation with said cooling unit for defrosting purposes, a reservoircontaining the defrosting fluid, electrically operated immersion heater means for heating the fluid in said reservoir, and motor driven pump means for circulating the heated fluid from said reservoir and through said duct system.

2. A refrigerating apparatus having a cooling unit susceptible of becoming frosted, defrosting means comprising a duct system for the application of a defrosting fluid in heat exchange relation with said cooling unit for defrosting purposes, a reservoir containing the defrosting fluid, means for heating the fluid in said reservoir, circulating means operable to deliver heated fluid from said reservoir and through said duct system, a timer, and means for electrically energizing said heating and circulating means at intervals under the control of said timer.

3. A refrigeratin apparatus having a cooling unit susceptible of becoming frosted, defrosting means comprising a duct system for the application of a defrosting fluid in heat exchange relation with said cooling unit for defrosting purposes, a reservoir containing the defrosting fluid, means for heating the fluid in said reservoir, circulating means operable to deliver heated fluid from said reservoir and through said duct system, a timer, means for electrically energizing said heating and circulating means at intervals under the control of said timer, and thermostatic means for disabling the defrosting means after said cooling unit reaches defrosted condition. 7

4. A refrigerating apparatus having a cooling unit susceptible of becoming frosted, electrically operated refrigerating means for circulating a fluid refrigerating medium to said unit for the abstraction of heat therefrom, a cooling control switch operable to control the delivery of electrical power to said refrigerating means, electrically actuated heating means for heating a defrosting medium, electrically actuated circulating means for delivering the heated defrosting medium in heat exchange relation with said cooling unit for defrosting purposes, a heating control switch operable to control the delivery of actuating power to said heating means, a de frosting control switch for controlling the operation of said circulating means, and means for opening and closing said cooling and defrosting switches alternately and for operating said heating switch prior to the operation of said defrosting switch.

5. A refrigerating apparatus having a cooling unit susceptible of becoming frosted, electrically operated refrigerating means for circulating a fluid refrigerating medium to said unit for the abstraction of heat therefrom, a cooling control switch operable to control the delivery of electrical power to said refrigerating means, electrically actuated heating means for heating a defrosting medium, electrically actuated circulating means for delivering the heated defrost ing medium in heat exchange relation with said cooling unit for defrosting purposes, a heating 10*- control switch operable to control thedelivery of actuating power to said heatingmeans, ade frosting control switch for controlling alternately thev operation of said. cooling control and heating control switches, timer means for actu ating said defrosting control switch atpredetermined intervals of time, and a thermally controlled switch for controllingthe circulationof the refrigerating medium to said cooling unit. I

6. A refrigerating apparatus having a cooling unitlsusceptible of becoming frosted, electrically operated refrigerating means for circulatinga fluid refrigerating medium to said unit for the ab'stractionof; heatl therefrom, a cooling control switchoperable'tdcontrol the delivery of electrical power to said refrigerating means, electrically actuated heating means for heating a defrosting medium, electrically actuated circulating means for delivering the heated defrost ing medium in heat exchange relation with said cooling unit for defrosting purposes, a heating control switch operable to control the delivery of actuating power to said heating means, a defrosting control switch for controlling alternately the operation of said cooling control and heating control switches, timer means for actuating said defrosting control switch at predetermined intervals of time, and a thermally controlled switch for controlling the circulation of the defrosting medium to said cooling unit.

7. A refrigerating apparatus having a cooling unit susceptible of becoming frosted, electrically operated refrigerating means for circulating a fluid refrigerating medium to said unit for the abstraction of heat therefrom, a cooling control switch operable to control the delivery of electrical power to said refrigerating means, electrically actuated heating means for heating a defrosting medium, electrically actuated circulating means for delivering the heated defrosting medium in heat exchange relation with said cooling unit for defrosting purposes, a heating control switch operable to control the delivery of actuating power to said heating means, a defrosting control switch for controlling alternately the operation of said cooling control and heatin control switches, timer means for actuating said defrosting control switch at predetermined intervals of time, and a thermally controlled switch for controlling the operation of said heating means.

- 8. A refrigerator, comprising an enclosed space to be cooled, a cooling unit in said space and having means forming a plurality of separate duct systems in said unit, includin a refrigerant duct system for the circulation of a refri erating medium in heat exchange relation with said unit for the abstraction of heat therefrom, a defrosting duct system for the circulation of a defrosting medium in heat exchange relation with said unit to heat the same for defrosting purposes, a circulating fan in said space, and means to operate said fan while the refrigerating medium is circulating in said refrigerant duct system and to discontinue fan operation when the defrosting medium is circulating in said defrosting duct system.

9. A refrigerator, comprising an enclosed space to be cooled, a coolin unit in said space and having means forming a plurality of separate duct systems in said unit, including a refrigerant duct system for the circulation of a refrigerating medium in heat exchange relation with said unit for the abstraction of heat therefrom, a defrosting duct system for the circulation of a 11 defrosting, medium .v in- 'heatdexchange .relation with said unit to heat the rsame 'for defrosting purposes, I a: circulating faniinnsaid. space,.means to operate .said fan while. the. refrigerating medium. is .circulatingdn said; refrigerant duct-.system and .to discontinue vfan. operation when the defrosting medium is circulating...in said; defrosting duct system, means forming 1 a drip (tray, 7 in said space, in position to ;receive, defrosted.1iquid ifrom. saidvunit, zandha. discharge. conduit connected with :said .tray and extending, outwardlyv of said space for v the delivery of defrosted liquid therefrom.

' .EREDAL-RICKERT. RQYLE. .CRIQH'I'QN.

REFERENCES CITED The following references are .of record in the file of this patent:

vUNITED STATES PATENTS Number Name Date 1,908,573 Sulzberger May 9, 1933 10 1,913,433 Doble, Jr June 13, 1933 2,266,373 Marlo Dec. 16,1941 12,433,574 Newton Dec. 30, 1947 

